The major merozoite surface antigen (gp195) of P. falciparum and its analogues in several other Plasmodia induces a protective immune response in simian and murine hosts and is a prime candidate for a blood-stage malaria vaccine. Yeast recombinant gp195-based polypeptides are being developed as vaccine antigens. The efficacy of such vaccines is dependent on their ability to induce the appropriate antigen-specific B cells and to efficiently stimulate T cells which serve as helper/inducer cells in the antibody response or in antibody-independent immune responses. The specific aims of this project are (1) to define B cell recognition sites involved in the antibody responses to gp195 and gp195-related polypeptides and to determine whether H-2-linked immune response (Ir) genes control responsiveness to these recognition sites, (2) to define T cell recognition sites, study their regulation by Ir genes, and determine the surface phenotype of T cells induced by gp195 and recombinant gp195-related polypeptides and synthetic peptides, (3) to generate gp195-specific T cell lines and characterize their fine specificity and function (T helper activity, production of gamma interferon), and (4) to relate B cell and T cell recognition sites to variable, conserved, or group- specific regions of gp195 molecules. B cell recognition sites will be defined by immunization of mice with parasite-purified gp195 and gp195-related polypeptides and evaluation of serum antibody specificity by an ELISA assay. T cell recognition sites will be similarly defined using the antigen-induced proliferation assay or antigen-specific T helper cell assays. Antigens to be used for specificity analyses are (1) the homologous parasite-purified gp195: (2) a heterologous parasite-purified gp195 differing in group specific regions from the homologous protein; (3) recombinant gp195-related polypeptides corresponding to different fragments of the complete gp195 protein; and (4) synthetic peptides corresponding to variable repeat regions and to potential immuno- dominant B cell or T cell epitopes predicted by appropriate computer algorithms. The possible influence of Ir genes on responsiveness to B cell and T cell recognition sites will be studied by comparing the B cell and T cell recognition sites utilized by mice differing only at H-2 linked Ir genes. The characterization of T cell and B cell recognition sites as variable, conserved or group-specific is particularly relevant to vaccine design and will be accomplished by comparing antigen specificity for the homologous versus the heterologous gp195 protein.